Evoked Unitary and Gross Electric Activity in the Cerebral Cortex in Early Prenatal Ontogeny

Abstract

DURING development, the form of the electrocortical surface response elicited by peripheral stimulation undergoes a series of typical changes which have been thought to reflect the functional maturation of the cerebral cortex. Most electrophysiological studies of the subject (for example, ref. 1), however, have been performed on post-natal animals, in which the structural and functional development of the cortex is comparatively advanced, so the very early stages of functional development have been largely neglected. Molliver² recently found that the somaesthetic response evoked by tactile stimulation of the nose in prenatal preparations of sheep is dominated by a surface positive deflexion at its earliest appearance, and that during the next developmental phase this potential displays a positive–negative configuration. Most developmental studies have been made using surface gross electrodes only. Recordings of evoked potentials and unitary neuronal activity at varying depths in the cortex should provide information about the accurate location of the changes observed with the surface recording. Furthermore, our concurrent recordings will help to reveal the sequence in which neurones in various cortical layers become activated by the afferent inflow during prenatal development. The aim of the present study was to investigate the early phase of functional cortical maturation; in other words, when the very first signs of cortical response to afferent stimulation become apparent.